Credit: USDA Forest Service, Pacific Northwest Region, State and Private Forestry, Forest Health Protection.
Collection: Bureau of Entomology Collection; La Grande, Oregon.
To learn more about this photo collection see:
Wickman, B.E., Torgersen, T.R. and Furniss, M.M. 2002. Photographic images and history of forest insect investigations on the Pacific Slope, 1903-1953. Part 2. Oregon and Washington. American Entomologist, 48(3), p. 178-185.
The following information about the Keen Classification system is excerpted from Wickman, Boyd E. 2005. Harry E. Burke and John M. Miller, pioneers in Western forest entomology. Gen. Tech. Rep. PNW-GTR-638. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 163 p.:
"Keen’s research on tree classification continued in Oregon and was called the “Keen Ponderosa Pine Tree Classification.” The Salman-Bongberg approach was called the “California Pine Risk-Rating System.” Both systems evolved from research on tree susceptibility to bark beetle attack that had been conducted in the 1920s by Miller, Keen, Patterson, Person, and Struble. Tree growth rates were a particularly important area of the studies, with Miller and Person proposing that slower growing mature ponderosa pine were more susceptible to attack by the western pine beetle than younger more vigorous trees (Smith et al. 1981).
The rating systems resulted in a silvicultural approach
to managing the western pine beetle instead of the direct
control method of felling infested trees, then peeling and
burning the bark. This was a breakthrough for forest managers that allowed them to capture the economic value of susceptible trees before they were killed by bark beetles, and at the same time resulted in decreased beetle populations or at least seemed to prevent outbreaks. The Salman- Bongberg California risk-rating system identified susceptible trees by assigning penalty points to crown and stem characteristics of a tree. This was followed up by a logging practice called sanitation salvage (Smith et al. 1981). The Keen system, involved four classes based on age and four vigor classes within each age class. It was oriented more toward identifying the susceptibility of individual trees to insect attack. Keen also assigned penalty points in his system. It was slightly more complex to use and was not directly tied to the sanitation salvage concept, but a certain level of logging of susceptible trees was generally followed. Keen’s classification was more widely used in ponderosa pine stands of eastern Oregon, and the California system was used for both ponderosa pine and Jeffrey pine stands in eastern California."
For more, see: www.fs.fed.us/pnw/publications/pnw_gtr638/